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JoinTable with additional column [message #932490]

Thu, 04 October 2012 06:32

Pavel Zelenka

Messages: 61
Registered: July 2009

Member

Hi,

I would appreciate a little help with OneToMany relation using JoinTable. I use EclipseLink 1.1.4

Let's say there are entities Person and Projects. There is a join table which connects projects to persons. But the join table has an additional column "is_valid". Is there any way to tell the EclipseLink to relate only those entities where is_valid=1?
Or the best way is to use entity class for the join table (http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Additional_columns_in_join_table)

Thanks

Pavel

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Re: JoinTable with additional column [message #932964 is a reply to message #932490]

Thu, 04 October 2012 16:05

Chris Delahunt

Messages: 1053
Registered: July 2009

Senior Member

While I'm usually against it because it hides data from your object model, there is a way to filter results for the mapping described here:
http://wiki.eclipse.org/EclipseLink/Examples/JPA/MappingSelectionCriteria

This allows you to add in the is_valid=1 to the queries bringing in the data for the mapping. It means though that your cache will not always represent what is in the database - changing is_valid may require the owning entity to be refreshed to have the changes reflected in the entity.

Unless the mapping is read-only though, you will need to map it somehow so it can be inserted into when entities are added to the collection. I usually recommend the Mapping_a_Join_Table_with_Additional_Columns approach because it reflects what is in the database, and allows the application to decide what to display. The entity can transparently filter results to the app with say a getValidEntities method, and allows for queries using the is_valid field if required in the future.

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